Abstract

CMOS image sensors (CIS) are promising candidates as part of optical imagers for the plasma diagnostics devoted to the study of fusion by inertial confinement. However, the harsh radiative environment of Megajoule Class Lasers threatens the performances of these optical sensors. In this paper, the vulnerability of CIS to the transient and mixed pulsed radiation environment associated with such facilities is investigated during an experiment at the OMEGA facility at the Laboratory for Laser Energetics (LLE), Rochester, NY, USA. The transient and permanent effects of the 14 MeV neutron pulse on CIS are presented. The behavior of the tested CIS shows that active pixel sensors (APS) exhibit a better hardness to this harsh environment than a CCD. A first order extrapolation of the reported results to the higher level of radiation expected for Megajoule Class Laser facilities (Laser Megajoule in France or National Ignition Facility in the USA) shows that temporarily saturated pixels due to transient neutron-induced single event effects will be the major issue for the development of radiation-tolerant plasma diagnostic instruments whereas the permanent degradation of the CIS related to displacement damage or total ionizing dose effects could be reduced by applying well known mitigation techniques.

Figures (14)

(a) CAD drawing of the Experimental Hall (EH) of the Laser Megajoule facility. The EH diameter is 30 m whereas the diameter of the target chamber is 10 m. (b) Neutron and gamma fluxes at the locations of diagnostic components during full performance shots in LMJ, from [8].

Raw dark frames: (a) before a shot. (b) during shot 8 and (c) right after shot 8. Neutron fluence at the detector level: 7 × 106 n/cm2. The image contrast has been tuned to emphasize the studied effects.

Reconstituted dark frame during laser shot 8 with subtracted average dark level. (a) before a shot. (b) during the shot. (c) magnification of an area of the reconstituted image taken during a shot (indicated by a white dashed square in (b). The image contrast has been tuned to emphasize the studied effects.

Raw dark frame (200 × 200 pixel window at the top left corner of the pixel array) taken at room temperature (a) before the first shot and (b) after the last shot showing the creation of a few permanent hot pixels. The image contrast has been tuned to emphasize the studied effects.